High-frequency substrate and production method therefor

Abstract

The high-frequency substrate is constructed of a base member and a conductor adhered to the base member, and the base member is composed of a polymer which is a fluoropolymer having a conductor-affinitive monomer graftpolymerized at a grafting percentage of 1% or less by weight. After reactive sites necessary for graftpolymerization are formed on a film of a fluoropolymer under an oxygen-free atmosphere by irradiating the film with an electron beam or the like, the fluoropolymer film is introduced into a solution of a conductor-affinitive monomer so as to cause graftpolymerization, and a conductor is adhered thereto to thereby produce a substrate, with a grafting percentage of the monomer to the fluoropolymer being 1% or less by weight in the graftpolymerization. The technique leads to the production of a high-frequency substrate having superior adhesion force with respect to the conductor.

1. A high-frequency substrate constructed of a base member and a conductor adhered to the base member, wherein the base member is composed of a fluoropolymer of polytetrafluoroethylene or tetrafluoroethylene-hexafluoropropylene copolymer, the fluoropolymer having a conductor-affinitive monomer of acrylic acid graftpolymerized thereto at a grafting percentage of 0.01%-1% by weight of the fluoropolymer before graftpolymerization. 
     
     
       2. The high-frequency substrate as claimed in  claim 1 , wherein the conductor is copper and includes an electrically conductive circuit or wiring. 
     
     
       3. A method for producing a high-frequency substrate, constructed of a base member and a conductor adhered to the base member, wherein the base member is composed of a polymer which is a fluoropolymer film having a conductor-affinitive monomer graftpolymerized thereto, which comprises the steps of:
 (I) forming reactive sites necessary for graftpolymerization, on the film of fluoropolymer under an oxygen-free atmosphere, wherein the fluoropolymer has a thickness of 100 μm to 500 μm, and wherein the reactive sites are formed by applying an electron beam to the fluoropolymer film, with a radiation dose of from 5 to 100 kGy, an acceleration voltage of from 2 MeV to 3 MeV, and a current of from 1.0 mA to 2.0 mA, 
 (II) introducing the fluoropolymer film having the reactive sites thereon, into an oxygen-free solution in which a conductor-affinitive monomer is dissolved, so as to graftpolymerize the monomer to the fluoropolymer, wherein the grafting is carried out at a graftpolymerization percentage of the monomer to the fluoropolymer of 0.01%-1% by weight of the fluoropolymer before graftpolymerization the fluoropolymer is polytetrafluoroethylene or tetrafluoroethylene-hexafluoropropylene copolymer, and the monomer is acrylic acid, and 
 (III) adhering a conductor to the surface of the film of the fluoropolymer after the graftpolymerization. 
 
     
     
       4. The method for producing the high-frequency substrate as claimed in  claim 3 , wherein the step (III) of conductor adhering is carried out by sputtering. 
     
     
       5. The method of for producing the high-frequency substrate as claimed in  claim 3 , wherein the method further includes the step of immersing the fluoropolymer film after the graftpolymerization in a solution of conductor, thereby rendering the conductor adsorbed on the surface of the fluoropolymer film after the graftpolymerization. 
     
     
       6. The method for producing the high-frequency substrate as claimed in  claim 1 , wherein the grafting percentage is calculated as [(weight of fluoropolymer after graftpolymerization-weight of fluoropolymer before graftpolymerization)/(weight of fluoropolymer before graftpolymerization)]×100. 
     
     
       7. The high-frequency substrate as claimed in  claim 1 , wherein the fluoropolymer comprises a film having a thickness of 100 μm to 500 μm. 
     
     
       8. A high-frequency substrate constructed of a base member and a conductor adhered to the base member, wherein the base member is composed of a fluoropolymer film of polytetrafluoroethylene or tetrafluoroethylene-hexafluoropropylene copolymer, the fluoropolymer film having acrylic acid monomer graftpolymerized thereto at a grafting percentage of 0.01%-1% by weight of the fluoropolymer before graftpolymerization, the high-frequency substrate being formed by a method which comprises:
 forming reactive sites on a fluoropolymer layer comprising irradiating the fluoropolymer layer with an electron beam which cleaves fluorine-carbon bonds to form the reactive sites; and 
 thereafter, introducing the fluoropolymer film having the reactive sites thereon into an oxygen-free solution in which acrylic acid is dissolved; and 
 graftpolymerizing the acrylic acid monomer to the fluoropolymer at a grafting percentage of 0.01%-1% by weight of the fluoropolymer before graftpolymerization. 
 
     
     
       9. The method for producing the high-frequency substrate as claimed in  claim 3 , wherein the grafting percentage is calculated as [(weight of fluoropolymer after graftpolymerization-weight of fluoropolymer before graftpolymerization)/(weight of fluoropolymer before graftpolymerization)]×100.